Richard Dawkins examines sin. He asks whether the old religious rules about what isright and wrong are helpful and explores what science can tell us abouthow to be good.

Dawkins journeys from riot-torn inner city London to America's Bible Belt, building a powerful argument that religion'sabsolutist moral codes fuel lies and guilt.

He finds the most extreme example in a Paris plastic surgery clinic that specialises inmaking Muslim brides appear to be virgins once again.

But what can science and reason tell us about morality? Through encounters withlemurs, tango dancers, the gay rights campaigner Matthew Parris and thescientist Steven Pinker, Dawkins investigates the deeper roots of moralbehaviour in our evolutionary past.

He explores the rituals that surround mating and the science of disgust and taboo. Drawing on crimedata and insights from neuroscience, he argues that our evolved sensesof reason and empathy appear to be making us more and more moral, evenas religious observance declines.